Dry process for making synthetic fiber paper



July 19, 1966 H. w. coATEs 3,261,899

DRY PROCESS FOR MAKING SYNTHETIC FIBER PAPER Filed Nov. 27, 1962 United States Patent O 3,261,899 DRY PRGCESS FOR MAKING SYNTHETIC FIBER PAPER Herbert W. Coates, Fairfax, Ala., assigner to Celanese Corporation of America, New York, NSY., a corporation of Delaware Filed Nov. 27, 1962, Ser. No. 242,865

2 Claims. (Cl. 264-123) This application is a continuation-in-part of copending application, Ser. No. 67,763, filed November 7, 1960, now U.S. Patent No. 2,914,422.

This -invention relates to paper products and more particula-rly to paper materials produced by a novel dry paper making process.

Papers are conventionally made by wet processes in which the fibrous material which is made into a paper sheet is first dispersed in water. Papers made by these conventional processes are usually limited to the type of fibrous materials lhaving fiber lengths of less .than 1/2 inch.

It is an object of this invention to provide a novel process for making paper.

It is another object of this invention to provide a novel process for making paper which does not use water.

It is a further object of this invention to provide a novel process for making a novel paper which has fiber lengths greater than 1/2 inch.

It is a further object of this invention to provide paper having a high Wet strength.

Other objects and advantages of this invention will become app-arent from the following description and claims in which all proportions are by weight unless otherwise specified.

In accordance with one aspect of the present invention there is provided a process for `making a paper which comprises applying to thermoplastic fibers, a plasticizer for said fibers, forming .a non-woven web comprising said thermoplastic fibers and calendering said web.

The process of this invention employs external application of the plasticizer as distinguished from internal plasticization in which the fiber when originally produced already has the plasticizer incorporated therein. I have found that external plasticizat-ion is less expensive in that smaller quantities o-f plasticizer are needed. In addition, external plasticizatio-n results in a paper having higher resistance to deformation by temperature and/ o1' pressure, higher resilience and recovery properties and a minimum tendency towards delamination.

When external plasticization is used, itis very important that the applied plasticizer be evenly distributed throughout the fiber mass, that is, the maximum number of fibers should be coated with plasticizer. It is, therefore, preferred to apply the plasticizer to the fibers prior to the non-Woven web formation. Since the staple fibers used in the process of this invention usually are produced in a compacted form as in bales or in `tufts c-ut from a tow, it is most advantagous to open or loosen the comp-acted fibers before the application of the plasticizer. The compacted liber may be opened in any conventional manner such as carding, picking, by a staple liber opener, or by a waste opener. After opening, the platsicizer may be conveniently applied by spraying, fogging, misting, or volatilizing. It has been found particularly advantageous to simultaneously open and apply the plasticizer to the compacted fibers. This may be 'accomplished in the hopper of a Rando Feeder having associated therewith apparatus for spraying plasticizer into the liber rnass in the hopper. The compacted fibers are fed into the hopper of -the Rando Feeder where they are opened fby continuous agitation.

The Rando Feeder and Webber referred to is a commerical Webber and feeder, a drawing of which may be 3,261,899 Patented July 19, 1966 ICC found on p. 484 of The Man-Made Textile Encyclopedia published by Textile Book Publishers in 1959. The agitation in the Rando Feeder is furnished .by a plurality of moving aprons, which may contain picks or other similar projections lon their surfaces. These moving aprons act upon and circulate the compacted fiberA mass in the hopper. Simultaneously with the opening, the spraying apparatus applies a fine mist of plasticizer onto the fibrous mass. The cont-inued agitation of the fiber mass after the application of plasticizer insure-s thorough plasticizer distribution throughout the fiber mass. The amount of time for which the liber mass is preferably subjected to .agitation and plasticizer application will vary with the fiber denier. High denier fibers consist of fewer bers per pound and require less time, c g., 5.5 denier cellulose acetate fiber requires .approximately three times as much time as do 17 denier fibers of the same material. With fiber masses containing cellulose acetate bers, the time for the simultaneous plasticizer application and agitation advantageously is from 1/2 minute to 15 minutes, and most preferably from 2 to 5 minutes. I-n the case where the thermoplastic fibers are to be blended with another thermoplastic or non-thermoplastic fiber, the fibers to be blended are preferably blended simultaneously with the opening of the thermoplastic fibers.

The applied plasticizer advantageously constitutes from 5 to 40% of the fiber weight, most preferably from 8 to 15% of the Weight.

'The blended and plasticized fibrous mass is then formed into a web. While the web yformation may be accomplished in any conventional manner such as carding, garnetting, air deposition, picking, or garnetting and air doffng, where the opening and plasticization is performed in a Rando Feeder, the web is preferably lformed in a Rando Webber. In web formation, the number of fiber cross-over points available per .unit area will determine the overall character of the structure. A random fiber distribution having a maximum number of contacts per unit area is preferable in the web as it provides a better bonded structure than does a highly oriented or parallelized fiber construction.

The rweb `formed is then calendered bet-Ween a pair of calendering rolls at a pressure preferably of from about 10 to 50 tons expression and most preferably from about l5 to 25 tons expression, when using rolls having a fifty inch contact length, Preferably the rolls are a steel roll and a cotton fil roll. The extent of bonding in the nonwoven web increases with increased pressures, increased temperatures and lower calender roll speeds. At the roll pressures given above, suitable temperatures to which the materials are preferably heated during the calendering Will vary with the thermoplastic fibers used. For example, using cellulose esters such as cellulose acetate or triacetate at the above calendering pressures, the web is advantageously heated to from F. to 375 F. during calendering and preferably from 200 F. to 300 F. In order to heat the web to such temperatures, the calendering rolls are preferably heated to temperatures in the range of from about 300 F. to 400 F. The dwell time of the web in the nip ofthe calendering rollers is a very important factor in determining the nature of the paper produced. Too short a dwell time will result in a poorly bonded hairy type of paper While too -long a dwell time will result in a non-fibrous plastic-like sheet. The swell time is, of course, directly dependent upon the roller speed. At the above temperatures, preferable dwell times result when the speed of the calender rolls range from ll to 30 feet per minute and most preferably from 10 to l5 feet per minute.

In the cases where the required production speeds make it neces-sary `for the calendering rollers to rotate at speeds =higher than the preferred ranges which provide suitable dwell times, it has been found advantageous to employ more than one set of calendering rolls in tandem.

Further, it has been found to be advantageous Particularly in shortening required dwell times to pre-heat the web prior to calendering. The heat may be applied by any conventional means, eg., passing the web under infrared lights. It has been found to be particularly advantageous if steam is applied to the web just prior to calendering. In addition to its heating effect, steam acts as a plasticizer for some thermoplastic fibers such as cellulose acetate.

Embossing type of calendering may be substituted for smooth roll calendering to produce an embossed paper.

The web may be composed in whole or in part of thermoplastic fibers, representative examples of which include polyamides such as nylon, polyesters such as polyethylene terephthalate, acrylonitrile polymers and copolymers, olefin and olefinic ester polymers and copolymers such as polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, and the like. Especially good results are achieved with organic acid esters of cellulose such as cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate formate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate and the like. Of these, cellulose acetate is preferred, particularly cellulose acetate having an acetyl value from about 52 to 58% calculated as combined acetic acid. The thermoplastic A fibers advantageously comprise at least of the web.

The web may also include non-thermoplastic fibers such as cotton, rayon, wool, jute, wood pulp, ramie and silk.

The plasticizer remaining in the calendered web is preferably from 5 to 15% of the weight of the web and most preferably from 2 to 5% of the weight.

The component fibers, both thermoplastic and nonthermoplastic may be crimped or straight, range in denier preferably from 0.6 to 50 denier per fil and most preferably from 5.5 to 35.0 `denier per fil and have fiber llength advantageously from 0.5 to 3 inches and most preferably from 1.5 to 2 inches. While staple fibers are preferred in the practice of this invention, continuous filament fibers and even fibers spun into yarns may be used in the web of this invention.

In this latter respect, the process of this invention may produce paper containing staple fibers Agreater than 1/z inch as well as continuous fibers and yarns while paper produced by conventional wet process comprises fibers limited in length to under 1/z inch. Such increased fiber lengths provide novel papers having increased strength, particularly when wet.

The plasticizer employed in accordance with this invention may be of any suitable composition and may or may not be volatile. For example, if the thermoplastic fiber yarn is cellulose acetate, the preferred plasticizers include high boiling esters of polyhydric alcohols such as diacetin, glycol diacetate and triacetin, high boiling esters of carboxylic acids such as :alkyl or aryl esters of citric acid, adipicacid, maleic `acid and phthalic acid which include dimethyl phthalate, triethyl citrate and dibutyl phthalate, organic esters of inorganic acids such as tributyl phosphate, triethyl and tripropyl phosphate, tricresyl phosphate and trichloroethyl phosphate, alkoxy alkyl esters of inorganic acids such as methoxy ethyl chloride or of organic polybasic acids such as dimethoxy ethyl phthalate, dimethoxy ethyl adipate, dimethoxy ethoxy ethyl adipate and methyl phthalyl ethyl glycollate as well as orthoand para-N-ethyl toluene sulfonamides and high boiling 'ethers such as butyl ether of ethylene glycol, methyl ether of ethylene glycol, etc. The plasticizer may also comprise plasticizing meterials which `are solvents for the thermoplastic materials. Such a plasticizing material should be used under conditions under which it is incapable of effecting any appreciable dissolution of the non-woven material, i.e., it is applied in very small proportion relative to the thermoplastic material or it is employed diluted with non-solvents. Plasticizing materials in this category are preferably volatile, such as acetone or methylene chloride which may 'oe used for cellulose esters.

It is preferable that the contact time between the thermoplastic fiber and the plasticizer be held to a minimum. The contact time is the time between the application of the plasticizer and the calendering step. For example, with plasticizers activated at room temperature such as diacetm, acetone and methylene chloride used for cellulose acetate, the contact time is preferably less than 30 seconds. However, with other plasticizers such as dimethoxyethyl phthalate or dimethoxy ethoxy ethyl adipate the Contact time may be as high as 30 minutes.

The novel papers produced by the process of this invent'iorli1 contain staple fibers having lengths greater than 1/2 mc The papers may also contain yarns or continuous filament fibers. The individual fibers are bent, rolled and tumbled against each other. During calendering, the plasticizer remains substantially close to the fiber surface. Weight of the paper per square yard can vary over wide limits; preferably the weights range from 0.15 to 5.0 ounces per square yard and most preferably from 1.0 to 3.0 ounces per square yard. The papers preferably range in thickness from 1 to 7 mils and most preferably from 2 to 5 mils. The density of the paper can also'vary widely depending upon the strength and porosity required of the end product. The papers preferably have a density ranging from about 15 to 75% and most preferably 25 to 50% of that of a solid block of the same size made of the same materials in the same proportions as that in the paper, the difference indicating the proportion of air spaces in the paper, i.e., the porosity which ranges from about 25 to 85% and preferably 50 to 75%.

This invention will be more fully understood if reference is made to the accompanying drawing which is a diagrammatic view of apparatus for carrying out the process of this invention.

The compacted fibers 10 are opened, and blended in Rando Feeder hopper 11 while simultaneously being sprayed with plasticizer from sprayer 12. The plasticized fibers 13 are then conveyed by conveyor 14 to a web former 15 which may be a Rando Webber in which nonwoven fibrous web 16 is formed. Steam applicator 17 applies steam to the web and the web is then passed between calender rolls 18 and 19 to form paper 20 which is rolled on takeup roll 21.

As is implicit in the foregoing description, the process of this invention is essentially a dry process, i.e., the mass of fibers which are calendered to form the paper or relatively thin non-woven structure, are not suspended or slurried in any liquid such as water as in ordinary paper-making processes. Rather, the web to be calendered is deposited from a dry appearing mass of fibers, which are substantially surrounded by air or some other gas, e.g., an inert gas such as nitrogen, or carbon dioxide, if it is desired for any reason to carry out the process in the absence of oxygen. However, the fact that the process may be characterized as dry, does not, of course, preclude from the surfaces of the individual fibers such liquids as the plasticizer applied during the process or some Water deposited as a result of the normal Water vapor content of the air.

The following examples will illustrate the practice of this invention.

Example 1 Using the equipment shown in the drawing, baled crimped secondary cellulose acetate staple fibers having an acetyl value of 54% calculated as acetic acid, a fiber length of 2 inches and a denier of 17 and an equal proportion of baled secondary cellulose acetate staple fibers having an acetyl value of 54% calculated as acetic acid, a fiber length of 2 inches and denier of 5.5 were simultaneously fed into a Rando Feeder equipped with spraying apparatus where the bers were opened and blended by agitation for about 3 minutes .and sprayed simultaneously with a line mist of dimethoxy ethyl phthalate, the Weight of dimethoxy ethyl phthalate applied being 15% of the total liber weight. The libers were then passed through a Rando Webber wherein the libers were formed into a web. The web was then passed between a pair of calender rolls having a contact length of 50 inches, one of which was made of steel and the other of cotton lil at a linear speed of 13.5 feet per minute and a force of 15 tons expression, the steel roll having a temperature of 240 F. and the cotton roll, a temperature of 180 F. The paper produced weighed 1.1 ounces per square yard, was 3.5 mils thick, had a porosity of 75%. The paper produced was tested as to tear strength and burst strength in both the wet and dry condition and found not to show any decrease in these strengths inthe wet condition.

Example II Using the equipment shown in the drawing, baled crimped secondary cellulose acetate staple fibers having an acetyl value of 54% calculated as acetic acid, a liber length of 2 inches and a denier of 17 and an equal proportion of baled secondary cellulose acetate staple bers having an acetyl value of 54% calculated as acetic acid, .a liber length of 1%5 inches and denier of 5 .5 were simultaneously fed into a Rando Feeder equipped with spraying apparatus where the bers were opened and blended by agitation and sprayed simultaneously with a line mist of dimethoxy ethyl phthalate, the weight of dimethoxy ethyl phthalate applied being of the total liber weight. The libers were then passed through a Rando Webber wherein the bers were formed into a web. The web was then passed between a pair of calender rolls having a contact length of lifty inches, one of which was made of steel and the other of cotton fil at a linear speed of 7.5 feet per minute and a force of tons expression the steel roll having a temperature of 280 F. and the cotton roll, a temperature of 200 F. The paper produced weighs 3.0 ounces per square yard and is 6.7 mils thick .and has a porosity of 62%. The paper produced was tested as to tear strength and burst strength in both the wet and dry condition and found not to show any decrease in these strengths in the wet condition.

Example III Using the equipment shown in the drawing, baled crimped secondary cellulose acetate staple bers having an acetyl value of 54% calculated as acetic acid, a liber length 19/16 inches and a denier of 5.5 was fed into a Rando Feeder equipped with spraying apparatus where the fibers were opened and blended by agitation and sprayed simultaneously with a ne Imist of dimethoxy ethyl phthalate, the weight of dimethoxy ethyl phthalate applied being 12% of the total fiber weight. The libers were then passed through a Rando Webber wherein the libers were formed into a web. The web was then subjected to infra-red heating at a temperature of 200 F. for 30 seconds and then passed between a pair of calender rolls having a contact length of 50 inches, one of which was made of steel and the other of cotton lil at a linear speed of 12 feet per minute and a force of 15 tonsv Example IV Using the equipment shown in the drawing, 65 parts of baled secondary cellulose acetate staple bers having an acetyl value of 54% calculated as acetic acid, a liber length of 19/16 inches aind a denier of 5.5. are fed into a Rando Feeder equipped with spraying apparatus where the libers were opened and simultaneously sprayed with a line mist of dimethoxy ethyl phthalate, the weight of dimethoxy ethyl phthalate applied being 15% of the liber weight. The mixture was -allowed to stand for 1 hour and then was blended with 35 parts of wood pulp. The mixture was then formed into a web on a Rando Webber. The web was then passed between a pair of calender rolls, having a contact length of 50 inches one of which was made of steel and the other of cotton fil at a linear speed of 13.5 feet per minute and a force of 15 tons expression, the steel roll having a tempera-ture of 300 F. The paper produced weighs 3.2 ounces per square yard, is 6.0 mils thick and has a porosity of 55%. The paper produced was tested as to tear strength and burst strength in both the wet and dry condition and found not to show any decrease in these strengths in the wet condition.

Example V Example I was repeated using equal proportions of secondary cellulose acetate staple libers having -an acetyl value of 54% calculated as acetic acid, a liber length of 2 inches and a denier of 5 and polyethylene terephthalate bers having a liber length of 2 inches and a denier of 5 instead of the fibers of Example I. The web was subjected to infra-red heating at a temperature of 180-200 F. for 30 seconds just pnior to being calendered between a steel roll having a temperature of 300 F. and a cotton roll at a temperature of 215 F. This paper produced weighs 3.1 ounces per square yard, is 6 mils thick and has density of 42% and a porosity of 58 The paper produced was tested as to tear strength and burst strength in both the wet and dry condition and found not to show any decrease in these strengths in the wet condition.

It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described `my invention what I desire .to secure by Letters Patent is:

1. A substantially dry process for making paper which comprises: 1) applying from 5% to 40% by weight of a plasticizer selected from the group consisting of esters of polyhydric alcohols, esters of carboxylic acids, organic esters of inorganic acids, alkoxy alkyl esters of inorganic acids, and esters of organic polybasic lacids to opened staple libers composed of an organic acid ester of cellulose having a liber length exceeding 1/2 inch; (2) forming a nonwoven web comprising said libers having the plasticizer thereon; (3) calendering said web at a temperature of from F. to 375 F.; and (4) removing said web from the calender as synthetic paper having a porosity of from 25% to 85%.

2. Process according to claim 1 wherein said fibers are composed of cellulose acetate and said plasticizer is dimethoxy ethyl phthalate.

References Cited bythe Examiner UNITED STATES PATENTS 1,873,279 8/1932 Brown 156-372 2,493,194 1/1950 Heino 156-372 XR 2,586,105 2/1952 Speakrnan et al. 28-73 XR 2,869,973 1/ 1959 Hubbard et al 28-73 XR 2,961,361 11/1960 Dennis 156-372 XR OTHER REFERENCES Rando-Webber, Rando-Feeder Machines, Bulletin No. 101, Textile Division, Curlator Corporation, Rochester, N.Y., October 1950.

EARL M. BERGERT, Primary Examiner.

P. R. WYLIE, J. MATHEWS, Assistant Examiners. 

1. A SUBSTANTIALLY DRY PROCESS FOR MAKING PAPER WHICH COMPRISE: (1) APPLYING FROM 5% TO 40% BY WEIGHT OF A PLASTICIZER SELECTED FROM THE GROUP CONSISTING OF ESTERS OF POLYHYDRIC ALCOHOLS, ESTERS OF CARBOXYLIC ACIDS, ORGANIC ESTERS OF INORGANIC ACIDS, ALKOXY ALKYL ESTERS OF INORGANIC ACIDS, AND ESTERS OF ORGANIC POLYBASIC ACIDS TO OPENED STAPLE FIBERS COMPOSED OF AN ORGANIC ACID ESTER OF CELLULOSE HAVING A FIBER LENGTH EXCEEDING 1/2 INCH; (2) FORMING A MONWOVEN WEB COMPRISING SAID FIBERS HAVING THE PLASITICIZER THEREON; (3) CALENDERING SAID WEB AT A TEMPERATURE OF FROM 150*F. TO 375*F,; AND (4) REMOVING SAID WEB FROM THE CALENDER AS SYNTHETIC PAPER HAVING A POROSITY OF FROM 25% TO 85%. 